Regulation of autophagy and the ubiquitin-proteasome system by the FoxO transcriptional network during muscle atrophy

GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice

The survival rate for children and adolescents has increased to over 85%. However, there is limited understanding of the impact of pediatric cancers on muscle development and physiology. Given that brain tumors alone account for 26% of all pediatric cancers, this study aimed to investigate the skeletal muscle consequences of tumor growth in young mice. C2C12 myotubes were cocultured with GL261 murine glioblastoma cells to assess myotube size. GL261 cells were then injected subcutaneously into 4-wk-old male C57BL/6J mice. Animals were euthanized 28 days post-GL261 implantation. Muscle function was tested in vivo and ex vivo. Muscle protein synthesis was estimated via the SUnSET method, and gene/protein expression levels were assessed via Western blotting and qPCR. In vitro, the C2C12 cultures exposed to GL261 exhibited myotube atrophy, consistent with a disrupted anabolic/catabolic balance. In vivo, carcass, heart, and fat mass were significantly reduced in the tumor-bearing mice. Skeletal muscle growth was impeded in the GL261 hosts, along with a smaller muscle cross-sectional area (CSA). Both in vivo muscle torque and the ex vivo Extensor Digitorum Longus (EDL) muscle force were unchanged. At molecular level, the tumor hosts displayed reduced estimations of muscle protein synthesis and increased muscle protein ubiquitination, in disagreement with decreased muscle ubiquitin ligase mRNA expression. Overall, we showed that GL261 tumors impact the growth of pediatric mice by stunting skeletal muscle development, decreasing muscle mass, reducing muscle fiber size, diminishing muscle protein synthesis, and altering protein catabolism signaling.NEW & NOTEWORTHY This study shows that pediatric brain tumors stunt muscle development in young mice. GL261 glioblastoma cells caused myotube atrophy, reduced carcass, heart, and fat mass, and impeded skeletal muscle growth. Tumor-bearing mice had decreased muscle protein synthesis and increased protein ubiquitination. This is the first demonstration that GL261 tumors reduce muscle mass and fiber size, impair muscle function and innervation, and alter muscle protein turnover.

Relationship between skeletal muscle mass and prognosis in patients with liver cancer receiving targeted therapy: A meta-analysis

BACKGROUND

Many studies have found that sarcopenia is related to the survival of patients with liver cancer, which may lead to worse prognosis.

AIM

To investigate the relationship between skeletal muscle mass and prognosis in patients with liver cancer receiving targeted therapy by meta-analysis.

METHODS

PubMed, Embase, Cochrane Library, and Web of Science were searched for clinical studies on the relationship between skeletal muscle index (SMI) and the prognosis of patients with liver cancer receiving targeted therapy from inception to March 1, 2022. Meta-analysis and sensitivity analysis of the data were performed using Stata 16.0 software.

RESULTS

A total of 6877 studies were searched, and finally 12 articles with 1715 cases were included. Meta-analysis result of 8 articles showed that compared with non-low SMI group, the overall survival (OS) of patients with liver cancer in the low SMI group was significantly shorter (hazard ratio = 1.60, 95% confidence interval: 1.44-1.77, P = 0.000). Meta-analysis result of 4 articles showed that, compared with low SMI group, patients in the non-low SMI group had longer OS (hazard ratio = 0.59, 95% confidence interval: 0.38-0.91, P = 0.018).

CONCLUSION

Skeletal muscle mass is positively correlated with OS in patients with liver cancer receiving targeted therapy.

Deubiquitinating Enzyme USP2 Alleviates Muscle Atrophy by Stabilizing PPAR-γ

Insulin resistance, a hallmark of type 2 diabetes, accelerates muscle breakdown and impairs energy metabolism. However, the role of ubiquitin specific peptidase 2 (USP2), a key regulator of insulin resistance, in sarcopenia remains unclear. Peroxisome proliferator-activated receptor γ (PPAR-γ) plays a critical role in regulating muscle atrophy. The role of deubiquitinase USP2 in mitigating muscle atrophy was investigated. Our findings revealed reduced USP2 expression in skeletal muscles of patients with type 2 diabetes. In mouse models of diabetes- and dexamethasone (DEX)-induced muscle atrophy, USP2 expression was downregulated in skeletal muscles. Usp2 knockout exacerbated muscle loss and functional impairment induced by diabetes or DEX. Moreover, skeletal muscle-specific Usp2 knockout further aggravated muscle loss and functional impairment induced by diabetes. Local injection of adeno-associated virus-Usp2 into the gastrocnemius muscles of diabetic mice increased muscle mass and improved skeletal muscle performance and endurance. It enhanced insulin sensitivity in diabetic mice, shown by lower fasting serum glucose and insulin levels and better glucose tolerance. Mechanistic analysis showed USP2 directly interacted with PPAR-γ by deubiquitinating it, stabilizing its protein levels, enhancing insulin signaling and sensitivity, and maintaining muscle mass. Loss of PPAR-γ abolishes the regulatory effects of USP2 on insulin sensitivity and muscle atrophy. MYOD1 activates USP2 transcription by binding to its promoter region. This study demonstrates the protective role of USP2 in mitigating muscle atrophy by stabilizing PPAR-γ through deubiquitination, particularly in models of diabetic and DEX-induced muscle atrophy. Targeting the USP2-PPAR-γ axis may offer promising therapeutic strategies for metabolic disorders and sarcopenia.

ARTICLE HIGHLIGHTS

The Alleviative Effect of Sodium Butyrate on Dexamethasone-Induced Skeletal Muscle Atrophy

Skeletal muscle mass is significantly negatively regulated by glucocorticoids. Following glucocorticoid administration, the balance between protein synthesis and breakdown in skeletal muscle is disrupted, shifting towards a predominance of catabolic metabolism. Short-chain fatty acids like sodium butyrate have been found to regulate inflammatory reactions and successively activate signaling pathways. The preventive benefits of sodium butyrate against dexamethasone-induced skeletal muscle atrophy and myotube atrophy models were examined in this work, and the underlying mechanism was clarified. A total of 32 6-week-old C57BL/6 inbred male mice were randomly assigned to one of four groups and treated with dexamethasone to induce muscle atrophy and sodium butyrate. We found that sodium succinate alleviated dexamethasone-induced myotube atrophy in the myotube atrophy model by lowering the gene expression of two E3 ubiquitin ligases, Atrogin-1 and MURF1, and activating the AKT/mTOR signaling pathway. Pertussis toxin reversed this effect, indicating that G protein-coupled receptors were involved in sodium butyrate's action as a mediator. Additionally, pre-treatment with sodium butyrate lowered weight and muscle mass loss in a mouse model of skeletal muscle atrophy, dramatically decreased the MURF1 gene expression and decreased the nuclear translocation of the glucocorticoid receptor. In conclusion, this study shows that sodium butyrate inhibits the expression of atrophy genes, thus preventing the breakdown of proteins and the loss of muscle mass, while also inhibiting weight loss, in animal models.

Premature skeletal muscle aging in VPS13A deficiency relates to impaired autophagy

VPS13A disease (chorea-acanthocytosis), is an ultra-rare autosomal recessive neurodegenerative disorder caused by mutations of the VPS13A gene encoding Vps13A. Increased serum levels of the muscle isoform of creatine kinase associated with often asymptomatic muscle pathology are among the poorly understood early clinical manifestations of VPS13A disease. Here, we carried out an integrated analysis of skeletal muscle from Vps13a-/- mice and from VPS13A disease patient muscle biopsies. The absence of Vps13A impaired autophagy, resulting in pathologic metabolic remodeling characterized by cellular energy depletion, increased protein/lipid oxidation and a hyperactivated unfolded protein response. This was associated with defects in myofibril stability and the myofibrillar regulatory proteome, with accumulation of the myocyte senescence marker, NCAM1. In Vps13a-/- mice, the impairment of autophagy was further supported by the lacking effect of starvation alone or in combination with colchicine on autophagy markers. As a proof of concept, we showed that rapamycin treatment rescued the accumulation of terminal phase autophagy markers LAMP1 and p62 as well as NCAM1, supporting a connection between impaired autophagy and accelerated aging in the absence of VPS13A. The premature senescence was also corroborated by local activation of pro-inflammatory NF-kB-related pathways in both Vps13a-/- mice and patients with VPS13A disease. Our data link for the first time impaired autophagy and inflammaging with muscle dysfunction in the absence of VPS13A. The biological relevance of our mouse findings, supported by human muscle biopsy data, shed new light on the role of VPS13A in muscle homeostasis.

A FOX transcription factor phosphorylated for regulation of autophagy facilitates fruiting body development in Sclerotinia sclerotiorum

Autophagy is a recycling process by which eukaryotic cells degrade their own components, and the fruiting body (sexual structure) is a necessary structure for some plant pathogenic fungi to start the infection cycle. However, the transcriptional regulation of plant pathogenic fungal autophagy and autophagy regulating sexual reproduction remains elusive. Here, we provide the report linking autophagy transcription and fruiting body development in phytopathogenic fungi. The forkhead box transcription factor (FOX TF) SsFoxE2 in Sclerotinia sclerotiorum (Ss) binds to the promoters of ATG genes, thus promoting their transcription. SsFoxE2 is phosphorylated by AMP-activated protein kinase (AMPK) SsSnf1, and the phosphorylated SsFoxE2 interacts with (translationally controlled tumor protein) SsTctp1, leading to enhanced stability and ATG transcription activity of SsFoxE2. Importantly, the regulation of autophagy by SsFoxE2 affects the balance of the ubiquitination system and the early development of the fruiting body, which directly determines the occurrence and prevalence of plant disease. Furthermore, transcriptional binding of FOX TF to ATG gene promoters is conserved in phytopathogenic fungi. Taken together, our results bring new insights into pathogen initiation in phytopathogenic fungi and connect it to other autophagy-regulated processes in plant pathogens.

Dnmt3a overexpression disrupts skeletal muscle homeostasis, promotes an aging-like phenotype, and reduces metabolic elasticity

Mammalian aging is reportedly driven by the loss of epigenetic information; however, its impact on skeletal muscle aging remains unclear. This study shows that aging mouse skeletal muscle exhibits increased DNA methylation, and overexpression of DNA methyltransferase 3a (Dnmt3a) induces an aging-like phenotype. Muscle-specific Dnmt3a overexpression leads to an increase in central nucleus-positive myofibers, predominantly in fast-twitch fibers, a shift toward slow-twitch fibers, elevated inflammatory and senescence markers, mitochondrial OXPHOS complex I reduction, and decreased basal autophagy. Dnmt3a overexpression resulted in reduced muscle mass and strength and impaired endurance exercise capacity with age, accompanied by an enhanced inflammatory signature. In addition, Dnmt3a overexpression reduced not only sensitivity to starvation-induced muscle atrophy but also the restorability from muscle atrophy. These findings suggest that increased DNA methylation disrupts skeletal muscle homeostasis, promotes an aging-like phenotype, and reduces muscle metabolic elasticity.

Low-Carbohydrate Diet Exacerbates Denervation-Induced Atrophy of Rat Skeletal Muscle Under the Condition of Identical Protein Intake

BACKGROUND

While decreased protein intake is associated with muscle mass loss, it is unclear whether a decrease in carbohydrate intake adversely affects muscle atrophy independently of protein intake. Herein, we examined whether a low-carbohydrate (low-CHO) diet exacerbates denervation-induced muscle atrophy under conditions of identical protein intake.

METHODS

On day one of the experiment, male Wistar rats underwent unilateral denervation. The contralateral leg was used as the control. After denervation, rats were divided into two dietary groups: high-carbohydrate (high-CHO) and low-CHO. Each group was fed a high-CHO (70% carbohydrate) or low-CHO (20% carbohydrate) diet over 7 days. Total protein and energy intakes in both groups were matched by pair feeding. Rats were provided with deuterium oxide (D2O) tracer over the last 3 days of dietary intervention to quantify myofibrillar (muscle) protein synthesis (MPS).

RESULTS

Denervation reduced wet weight of the gastrocnemius muscle compared to the contralateral control (p < 0.05). Reductions in gastrocnemius muscle weight were greater in the low-CHO group (-34%) than the high-CHO group (-28%) (p < 0.05). Although denervation decreased MPS compared to the contralateral control (p < 0.05), no dietary effect on MPS was observed. Denervation resulted in increased mRNA and protein expression of Atrogin-1, a ubiquitin E3 ligase, compared to that in the contralateral control (p < 0.05). Increases in Atrogin-1 gene and protein expression due to denervation were greater in the low-CHO group than in the high-CHO group (p < 0.05).

CONCLUSIONS

We conclude that a low-CHO diet may exacerbate denervation-induced atrophy in fast-twitch-dominant muscles compared to a high-CHO diet, even when the same protein intake is maintained. Although blunted MPS contributed to muscle atrophy due to denervation, exacerbation of muscle atrophy by the low-CHO diet was not accompanied by explanatory changes in MPS. The effect of the low-CHO diet might be related to promotion of muscle-specific ubiquitin E3 ligase gene expression.

Astragaloside IV Improves Muscle Atrophy by Modulating the Activity of UPS and ALP via Suppressing Oxidative Stress and Inflammation in Denervated Mice

Peripheral nerve injury is common clinically and can lead to neuronal degeneration and atrophy and fibrosis of the target muscle. The molecular mechanisms of muscle atrophy induced by denervation are complex and not fully understood. Inflammation and oxidative stress play an important triggering role in denervated muscle atrophy. Astragaloside IV (ASIV), a monomeric compound purified from astragalus membranaceus, has antioxidant and anti-inflammatory properties. The aim of this study was to investigate the effect of ASIV on denervated muscle atrophy and its molecular mechanism, so as to provide a new potential therapeutic target for the prevention and treatment of denervated muscle atrophy. In this study, an ICR mouse model of muscle atrophy was generated through sciatic nerve dissection. We found that ASIV significantly inhibited the reduction of tibialis anterior muscle mass and muscle fiber cross-sectional area in denervated mice, reducing ROS and oxidative stress-related protein levels. Furthermore, ASIV inhibits the increase in inflammation-associated proteins and infiltration of inflammatory cells, protecting the denervated microvessels in skeletal muscle. We also found that ASIV reduced the expression levels of MAFbx, MuRF1 and FoxO3a, while decreasing the expression levels of autophagy-related proteins, it inhibited the activation of ubiquitin-proteasome and autophagy-lysosome hydrolysis systems and the slow-to-fast myofiber shift. Our results show that ASIV inhibits oxidative stress and inflammatory responses in skeletal muscle due to denervation, inhibits mitophagy and proteolysis, improves microvascular circulation and reverses the transition of muscle fiber types; Therefore, the process of skeletal muscle atrophy caused by denervation can be effectively delayed.

Functions and Therapeutic Potentials of Long Noncoding RNA in Skeletal Muscle Atrophy and Dystrophy

Skeletal muscle is the most abundant tissue in the human body and is responsible for movement, metabolism, energy production and longevity. Muscle atrophy is a frequent complication of several diseases and occurs when protein degradation exceeds protein synthesis. Genetics, ageing, nerve injury, weightlessness, cancer, chronic diseases, the accumulation of metabolic byproducts and other stimuli can lead to muscle atrophy. Muscular dystrophy is a neuromuscular disorder, part of which is caused by the deficiency of dystrophin protein and is mostly related to genetics. Muscle atrophy and muscular dystrophy are accompanied by dynamic changes in transcriptomic, translational and epigenetic regulation. Multiple signalling pathways, such as the transforming growth factor-β (TGF-β) signalling pathway, the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway, inflammatory signalling pathways, neuromechanical signalling pathways, endoplasmic reticulum stress and glucocorticoids signalling pathways, regulate muscle atrophy. A large number of long noncoding RNAs (lncRNAs) have been found to be abnormally expressed in atrophic muscles and dystrophic muscles and regulate the balance of muscle protein synthesis and degradation or dystrophin protein expression. These lncRNAs may serve as potential targets for treating muscle atrophy and muscular dystrophy. In this review, we summarized the known lncRNAs related to muscular dystrophy and muscle atrophy induced by denervation, ageing, weightlessness, cachexia and abnormal myogenesis, along with their molecular mechanisms. Finally, we explored the potential of using these lncRNAs as therapeutic targets for muscle atrophy and muscular dystrophy, including the methods of discovery and clinical application prospects for functional lncRNAs.

The role of AGEs in muscle ageing and sarcopenia

Sarcopenia is an ageing-related disease featured by the loss of skeletal muscle quality and function. Advanced glycation end-products (AGEs) are a complex set of modified proteins or lipids by non-enzymatic glycosylation and oxidation. The formation of AGEs is irreversible, and they accumulate in tissues with increasing age. Currently, AGEs, as a biomarker of ageing, are viewed as a risk factor for sarcopenia. AGE accumulation could cause harmful effects in the human body such as elevated inflammation levels, enhanced oxidative stress, and targeted glycosylation of proteins inside and outside the cells. Several studies have illustrated the pathogenic role of AGEs in sarcopenia, which includes promoting skeletal muscle atrophy, impairing muscle regeneration, disrupting the normal structure of skeletal muscle extracellular matrix, and contributing to neuromuscular junction lesion and vascular disorders. This article reviews studies focused on the pathogenic role of AGEs in sarcopenia and the potential mechanisms of the detrimental effects, aiming to provide new insights into the pathogenesis of sarcopenia and develop novel methods for the prevention and therapy of sarcopenia.

Transcriptomic adaptation of skeletal muscle in response to MICT and HIIT exercise modalities

Skeletal muscle exhibits remarkable plasticity in response to diverse stimuli, with exercise serving as a potent trigger. Varied exercise modalities, including moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT), induce distinct structural and functional adaptations on skeletal muscle. However, the underlying molecular mechanisms governing these adaptations remain poorly understood. In this study, we utilized RNA-seq to characterize the transcriptomic profile of murine gastrocnemius muscle following 8-week treadmill-based MICT (M group) and HIIT (H group). A total of 1052 DEGs were screened in H vs. M. Among the top 10 significant DEGs, Foxo1 and Myod1 are closely related to muscular physiology. Through KEGG pathway analysis, distinct adaptations were primarily identified in the FoxO, MAPK, and PI3K-AKT pathways. By analyzing the expression of myokines, a significantly higher Igf-1 expression level was observed in the M group compared to the H group. Therefore, IGF-1, a well-known upstream regulator of both the PI3K-AKT-FoxO and MAPK pathways, might drive distinct muscle adaptations through variations in Igf-1 expression induced by these two exercise modalities.

GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice

Introduction

The survival rate for children and adolescents has increased to over 85%. However, there is limited understanding of the impact of pediatric cancers on muscle development and physiology. Given that brain tumors alone account for 26% of all pediatric cancers, this study aimed to investigate the skeletal muscle consequences of tumor growth in young mice.

Methods

C2C12 myotubes were co-cultured with GL261 murine glioblastoma cells to assess myotube size. GL261 cells were then injected subcutaneously into 4-week-old male C57BL/6J mice. Animals were euthanized 28 days post-GL261 implantation. Muscle function was tested in vivo and ex vivo . Muscle protein synthesis was measured via the SUnSET method, and gene/protein expression levels were assessed via Western blotting and qPCR.

Results

In vitro , the C2C12 cultures exposed to GL261 exhibited myotube atrophy, consistent with a disrupted anabolic/catabolic balance. In vivo , carcass, heart, and fat mass were significantly reduced in the tumor-bearing mice. Skeletal muscle growth was impeded in the GL261 hosts, along with smaller muscle CSA. Both in vivo muscle torque and the ex vivo EDL muscle force were unchanged. At molecular level, the tumor hosts displayed reduced muscle protein synthesis and increased muscle protein ubiquitination, in disagreement with decreased muscle ubiquitin ligase mRNA expression.

Conclusions

Overall, we showed that GL261 tumors impact the growth of pediatric mice by stunting skeletal muscle development, decreasing muscle mass, reducing muscle fiber size, diminishing muscle protein synthesis, and altering protein catabolism signaling.

The role of chronic low-grade inflammation in the development of sarcopenia: Advances in molecular mechanisms

With the exacerbation of global population aging, sarcopenia has become an increasingly recognized public health issue. Sarcopenia, characterized by a progressive decline in skeletal muscle mass, strength, and function, significantly impacts the quality of life in the elderly. Herein, we explore the role of chroniclow-gradeinflammation in the development of sarcopenia and its underlying molecular mechanisms, including chronic inflammation-associated signaling pathways, immunosenescence, obesity and lipid infiltration, gut microbiota dysbiosis and intestinal barrier disruption, and the decline of satellite cells. The interplay and interaction of these molecular mechanisms provide new perspectives on the complexity of the pathogenesis of sarcopenia and offer a theoretical foundation for the development of future therapeutic strategies.

hBMSC-EVs alleviate weightlessness-induced skeletal muscle atrophy by suppressing oxidative stress and inflammation

BACKGROUND

Muscle disuse and offloading in microgravity are likely the primary factors mediating spaceflight-induced muscle atrophy, for which there is currently no effective treatment other than exercise. Extracellular vesicles derived from bone marrow mesenchymal stem cells (BMSC-EVs) possess anti-inflammatory and antioxidant properties, offering a potential strategy for combating weightless muscular atrophy.

METHODS

In this study, human BMSCs-EVs (hBMSC-EVs) were isolated using super-centrifugation and characterized. C2C12 myotube nutrition-deprivation and mice tail suspension models were established. Subsequently, the diameter of C2C12 myotubes, Soleus mass, cross-sectional area (CSA) of muscle fibers, and grip strength in mice were assessed to investigate the impact of hBMSC-EVs on muscle atrophy. Immunostaining, transmission electron microscopy observation, and western blot analysis were employed to assess the impact of hBMSC-EVs on muscle fiber types, ROS levels, inflammation, ubiquitin-proteasome system activity, and autophagy lysosome pathway activation in skeletal muscle atrophy.

RESULTS

The active hBMSC-EVs can be internalized by C2C12 myotubes and skeletal muscle. hBMSC-EVs can effectively reduce C2C12 myotube atrophy caused by nutritional deprivation, with a concentration of 10 × 108 particles/mL showing the best effect (P < 0.001). Additionally, hBMSC-EVs can down-regulate the protein levels associated with UPS and oxidative stress. Moreover, intravenous administration of hBMSC-EVs at a concentration of 1 × 1010 particles/mL can effectively reverse the reduction in soleus mass (P < 0.001), CSA (P < 0.01), and grip strength (P < 0.001) in mice caused by weightlessness. They demonstrate the ability to inhibit protein degradation mediated by UPS and autophagy lysosome pathway, along with the suppression of oxidative stress and inflammatory responses. Furthermore, hBMSC-EVs impede the transition of slow muscle fibers to fast muscle fibers via upregulation of Sirt1 and PGC-1α protein levels.

CONCLUSIONS

Our findings indicate that hBMSC-EVs are capable of inhibiting excessive activation of the UPS and autophagy lysosome pathway, suppressing oxidative stress and inflammatory response, reversing muscle fiber type transformation, effectively delaying hindlimb unloading-induced muscle atrophy and enhancing muscle function. Our study has further advanced the understanding of the molecular mechanism underlying muscle atrophy in weightlessness and has demonstrated the protective effect of hBMSC-EVs on muscle atrophy.

GDF15 Neutralization Ameliorates Muscle Atrophy and Exercise Intolerance in a Mouse Model of Mitochondrial Myopathy

BACKGROUND

Primary mitochondrial myopathies (PMMs) are disorders caused by mutations in genes encoding mitochondrial proteins and proteins involved in mitochondrial function. PMMs are characterized by loss of muscle mass and strength as well as impaired exercise capacity. Growth/Differentiation Factor 15 (GDF15) was reported to be highly elevated in PMMs and cancer cachexia. Previous studies have shown that GDF15 neutralization is effective in improving skeletal muscle mass and function in cancer cachexia. It remains to be determined if the inhibition of GDF15 could be beneficial for PMMs. The purpose of the present study is to assess whether treatment with a GDF15 neutralizing antibody can alleviate muscle atrophy and physical performance impairment in a mouse model of PMM.

METHODS

The effects of GDF15 neutralization on PMM were assessed using PolgD257A/D257A (POLG) mice. These mice express a proofreading-deficient version of the mitochondrial DNA polymerase gamma, leading to an increased rate of mutations in mitochondrial DNA (mtDNA). These animals display increased circulating GDF15 levels, reduced muscle mass and function, exercise intolerance, and premature aging. Starting at 9 months of age, the mice were treated with an anti-GDF15 antibody (mAB2) once per week for 12 weeks. Body weight, food intake, body composition, and muscle mass were assessed. Muscle function and exercise capacity were evaluated using in vivo concentric max force stimulation assays, forced treadmill running and voluntary home-cage wheel running. Mechanistic investigations were performed via muscle histology, bulk transcriptomic analysis, RT-qPCR and western blotting.

RESULTS

Anti-GDF15 antibody treatment ameliorated the metabolic phenotypes of the POLG animals, improving body weight (+13% ± 8%, p < 0.0001), lean mass (+13% ± 15%, p < 0.001) and muscle mass (+35% ± 24%, p < 0.001). Additionally, the treatment improved skeletal muscle max force production (+35% ± 43%, p < 0.001) and exercise performance, including treadmill (+40% ± 29%, p < 0.05) and voluntary wheel running (+320% ± 19%, p < 0.05). Mechanistically, the beneficial effects of GDF15 neutralization are linked to the reversal of the transcriptional dysregulation in genes involved in autophagy and proteasome signalling. The treatment also appears to dampen glucocorticoid signalling by suppressing circulating corticosterone levels in the POLG animals.

CONCLUSIONS

Our findings highlight the potential of GDF15 neutralization with a monoclonal antibody as a therapeutic avenue to enhance physical performance and mitigate adverse clinical outcomes in patients with PMM.

Pharmacological reduction of lipid hydroperoxides as a potential modulator of sarcopenia

We previously reported that elevated expression of phospholipid hydroperoxide glutathione peroxidase 4, an enzyme that regulates membrane lipid hydroperoxides, can mitigate sarcopenia in mice. However, it is still unknown whether a pharmacological intervention designed to modulate lipid hydroperoxides might be an effective strategy to reduce sarcopenia in aged mice. Here we asked whether a newly developed compound, CMD-35647 (CMD), can reduce muscle atrophy induced by sciatic nerve transection. We treated mice daily with vehicle or CMD (15 mg/kg, i.p. injection) starting 1 day prior to denervation. CMD treatment reduced hydroperoxide generation and blunted muscle atrophy by over 17% in denervated muscle. To test whether CMD can reduce ageing-induced muscle atrophy and weakness, we treated mice with either vehicle or CMD (15 mg/kg, i.p. injection) 3 days per week for 8 months, starting at 18 months of age until 26 months of age. We measured muscle mass, functional status of neuromuscular junctions, muscle contractile function and mitochondrial function in control and CMD-treated 26-month-old female mice. Treatment with CMD conferred protection against muscle atrophy in both tibialis anterior and extensor digitorum longus that was associated with maintenance of fibre size of MHC 2b and 2x fibres. Mitochondrial respiration was also protected in CMD-treated mice. We also found that muscle force generation was protected with CMD treatment despite denervation in ∼25% of the muscle fibres. Overall, this study shows that pharmacological interventions designed to reduce lipid hydroperoxides might be effective for preventing sarcopenia. KEY POINTS: Sarcopenia in aged mice is associated with muscle loss, contractile dysfunction, denervation, and reduced mitochondrial respiration. CMD-35647 is a pharmocological compound that can neutralize lipid hydroperoxides. 8 month treatment of CMD-35647 mitigated muscle atrophy in tibialis anterior and extensor digitorum longus. 8 month treatment of CMD-35647 improved muscle function in aged mice independent of the neuromuscular junction. Aged mice treated with CMD-35647 had greater respiration in red gastrocnemius muscle when compared to vehicle treated mice.

Transcriptional regulation of autophagy in skeletal muscle stem cells

Muscle stem cells (MuSCs) are essential for the regenerative capabilities of skeletal muscles. MuSCs are maintained in a quiescent state, but, when activated, can undergo proliferation and differentiation into myocytes, which fuse and mature to generate muscle fibers. The maintenance of MuSC quiescence and MuSC activation are processes that are tightly regulated by autophagy, a conserved degradation system that removes unessential or dysfunctional cellular components via lysosomes. Both the upregulation and downregulation of autophagy have been linked to impaired muscle regeneration, causing myopathies such as cancer cachexia, sarcopenia and Duchenne muscular dystrophy. In this Review, we highlight the importance of autophagy in regulating MuSC activity during muscle regeneration. Additionally, we summarize recent studies that link the transcriptional dysregulation of autophagy to muscle atrophy, emphasizing the dominant roles that transcription factors play in myogenic programs. Deciphering and understanding the roles of these transcription factors in the regulation of autophagy during myogenesis could advance the development of regenerative medicine.

The Bile Acid Metabolism of Intestinal Microorganisms Mediates the Effect of Different Protein Sources on Muscle Protein Deposition in Procambarus clarkii

The most economically important trait of the Procambarus clarkii is meat quality. Protein deposition is essential in muscle growth and nutritional quality formation. The effects and potential mechanisms of feed protein sources on crustaceans' muscle protein deposition have not been elucidated. This study established an all-animal protein source (AP) and an all-plant protein source group (PP), with a feeding period of 8 weeks (four replicates per group, 45 individuals per replicate). The results demonstrated that muscle protein deposition, muscle fiber diameter, and hardness were significantly higher in the PP group (p < 0.05). The transcript levels of genes involved in protein synthesis were notably upregulated, while those of protein hydrolysis and negative regulators of myogenesis notably downregulated in PP group (p < 0.05). Furthermore, protein sources shaped differential intestinal microbiota composition and microbial metabolites profiles, as evidenced by a significant decrease in g_Bacteroides (p = 0.030), and a significant increase in taurochenodeoxycholic acid (TCDCA) in PP group (p = 0.027). A significant correlation was further established by Pearson correlation analysis between the g_Bacteroides, TCDCA, and genes involved in the MSTN-mediated protein deposition pathway (p < 0.05). In vitro anaerobic fermentation confirmed the ability of the two groups of intestinal flora to metabolically produce differential TCDCA (p = 0.038). Our results demonstrated that the 'Bacteroides-TCDCA-MSTN' axis may mediate the effects of different protein sources on muscle development and protein deposition in P. clarkii, which was anticipated to represent a novel target for the muscle quality modulation in crustaceans.

Spotlight on the Mechanism of Action of Semaglutide

Initially intended to control blood glucose levels in patients with type 2 diabetes, semaglutide, a potent glucagon-like peptide 1 analogue, has been established as an effective weight loss treatment by controlling appetite. Integrating the latest clinical trials, semaglutide in patients with or without diabetes presents significant therapeutic efficacy in ameliorating cardiometabolic risk factors and physical functioning, independent of body weight reduction. Semaglutide may modulate adipose tissue browning, which enhances human metabolism and exhibits possible benefits in skeletal muscle degeneration, accelerated by obesity and ageing. This may be attributed to anti-inflammatory, mitochondrial biogenesis, antioxidant and autophagy-regulating effects. However, most of the supporting evidence on the mechanistic actions of semaglutide is preclinical, demonstrated in rodents and not actually confirmed in humans, therefore warranting caution in the interpretation. This article aims to explore potential innovative molecular mechanisms of semaglutide action in restoring the balance of several interlinking aspects of metabolism, pointing to distinct functions in inflammation and oxidative stress in insulin-sensitive musculoskeletal and adipose tissues. Moreover, possible applications in protection from infections and anti-aging properties are discussed. Semaglutide enhancement of the core molecular mechanisms involved in the progress of obesity and diabetes, although mostly preclinical, may provide a framework for future research applications in human diseases overall.

Spatheliachromen mitigates methylglyoxal-induced myotube atrophy by activating Nrf2, inhibiting ubiquitin-mediated protein degradation, and restoring mitochondrial function

BACKGROUND

Methylglyoxal (MGO) is a potent precursor of glycative stress that leads to oxidative stress and muscle atrophy in diabetes. Spatheliachromen (FPATM-20), derived from Ficus pumila var. awkeotsang, exhibited potential antioxidant activity.

PURPOSE

This study aimed to evaluate the potential impact and underlying mechanisms of FPATM-20 on MGO-induced myotube atrophy and mitochondrial dysfunction in mouse skeletal C2C12 myotubes.

METHODS

Atrophic and antioxidant factors were evaluated using immunofluorescence, enzyme-linked immunosorbent assay, and western blotting. Mitochondrial function was assessed using the ATP assay and Seahorse Cell Mito Stress Test. The glycogen content was determined using periodic acid-Schiff staining. Molecular docking was performed to determine the interaction between FPATM-20 and Keap1.

RESULTS

In myotubes treated with MGO, FPATM-20 activated the Nrf2 pathway, reduced ROS levels, enhanced antioxidant defense, and increased glycogen content. FPATM-20 improved myotube viability and size, upregulated myosin heavy chain (MyHC) expression, modulated ubiquitin-proteasome molecules (nuclear FoxO3a, atrogin-1, MuRF-1, and p62/SQSTM1), and inhibited apoptosis (Bax/Bcl-2 ratio and cleaved caspase 3). Moreover, FPATM-20 restored mitochondrial function, including mitochondrial membrane potential, mitochondrial oxygen consumption rate, and mitochondrial biogenesis pathway (nuclear PGC-1α/TFAM/FNDC5). The inhibition of Nrf2 with ML385 reversed the effects of FPATM-20 on MGO. Furthermore, molecular docking confirmed the binding of FPATM-20 to Keap1, a suppressor of Nrf2, showing the crucial role of Nrf2 in protective effects.

CONCLUSIONS

FPATM-20 protects myotubes from MGO toxicity by activating the Nrf2 antioxidant defense, reducing protein degradation and apoptosis, and enhancing mitochondrial function. Thus, FPATM-20 may be a novel agent for preventing skeletal muscle atrophy.

Role of AMP deaminase in diabetic cardiomyopathy

Diabetes mellitus is one of the major causes of ischemic and nonischemic heart failure. While hypertension and coronary artery disease are frequent comorbidities in patients with diabetes, cardiac contractile dysfunction and remodeling occur in diabetic patients even without comorbidities, which is referred to as diabetic cardiomyopathy. Investigations in recent decades have demonstrated that the production of reactive oxygen species (ROS), impaired handling of intracellular Ca2+, and alterations in energy metabolism are involved in the development of diabetic cardiomyopathy. AMP deaminase (AMPD) directly regulates adenine nucleotide metabolism and energy transfer by adenylate kinase and indirectly modulates xanthine oxidoreductase-mediated pathways and AMP-activated protein kinase-mediated signaling. Upregulation of AMPD in diabetic hearts was first reported more than 30 years ago, and subsequent studies showed similar upregulation in the liver and skeletal muscle. Evidence for the roles of AMPD in diabetes-induced fatty liver, sarcopenia, and heart failure has been accumulating. A series of our recent studies showed that AMPD localizes in the mitochondria-associated endoplasmic reticulum membrane as well as the sarcoplasmic reticulum and cytosol and participates in the regulation of mitochondrial Ca2+ and suggested that upregulated AMPD contributes to contractile dysfunction in diabetic cardiomyopathy via increased generation of ROS, adenine nucleotide depletion, and impaired mitochondrial respiration. The detrimental effects of AMPD were manifested at times of increased cardiac workload by pressure loading. In this review, we briefly summarize the expression and functions of AMPD in the heart and discuss the roles of AMPD in diabetic cardiomyopathy, mainly focusing on contractile dysfunction caused by this disorder.

Muscle aging and sarcopenia: The pathology, etiology, and most promising therapeutic targets

Sarcopenia is a progressive muscle wasting disorder that severely impacts the quality of life of elderly individuals. Although the natural aging process primarily causes sarcopenia, it can develop in response to other conditions. Because muscle function is influenced by numerous changes that occur with age, the etiology of sarcopenia remains unclear. However, recent characterizations of the aging muscle transcriptional landscape, signaling pathway disruptions, fiber and extracellular matrix compositions, systemic metabolomic and inflammatory responses, mitochondrial function, and neurological inputs offer insights and hope for future treatments. This review will discuss age-related changes in healthy muscle and our current understanding of how this can deteriorate into sarcopenia. As our elderly population continues to grow, we must understand sarcopenia and find treatments that allow individuals to maintain independence and dignity throughout an extended lifespan.

Deubiquitinases in skeletal muscle-the underappreciated side of the ubiquitination coin

Ubiquitination is a posttranslational modification that plays important roles in regulating protein stability, function, localization, and protein-protein interactions. Proteins are ubiquitinated via a process involving specific E1 activating enzymes, E2 conjugating enzymes, and E3 ligases. Simultaneously, protein ubiquitination is opposed by deubiquitinating enzymes (DUBs). DUB-mediated deubiquitination can change protein function or fate and recycle ubiquitin to maintain the free ubiquitin pool. Approximately 100 DUBs have been identified in the mammalian genome, and characterized into seven classes [ubiquitin-specific protease (USP), ovarian tumor proteases (OTU), ubiquitin C-terminal hydrolase (UCH), Machado-Josephin disease (MJD), JAB1/MPN/Mov34 metalloprotease (JAMM), Ub-containing novel DUB family (MINDY), and zinc finger containing ubiquitin peptidase (ZUP) classes]. Of these 100 DUBs, there has only been relatively limited investigation of 20 specifically in skeletal muscle cells, in vitro or in vivo, using overexpression, knockdown, and knockout models. To date, evidence indicates roles for individual DUBs in regulating aspects of myogenesis, protein turnover, muscle mass, and muscle metabolism. However, the exact mechanism by which these DUBs act (i.e., the specific targets of these DUBs and the type of ubiquitin chains they target) is still largely unknown, underscoring how little we know about DUBs in skeletal muscle. This review endeavors to comprehensively summarize the current state of knowledge of the function of DUBs in skeletal muscle and highlight the opportunities for gaining a greater understanding through further research into this important area of skeletal muscle and ubiquitin biology.

Tetrandrine induces muscle atrophy involving ROS-mediated inhibition of Akt and FoxO3

Tetrandrine (Tet), a well-known drug of calcium channel blocker, has been broadly applied for anti-inflammatory and anti-fibrogenetic therapy. However, due to the functional diversity of ubiquitous calcium channels, potential side-effects may be expected. Our previous report revealed an inhibitory effect of Tet on myogenesis of skeletal muscle. Here, we found that Tet induced protein degradation resulting in the myofibril atrophy. Upon administration with a relative high dose (40 mg/kg) of Tet for 28 days, the mice displayed significantly reduced muscle mass, strength force, and myosin heavy chain (MyHC) protein levels. The MyHC reduction was further detected in C2C12 myotubes after treating with Tet. Interestingly, the expression of Atrogin-1 and Murf-1, the skeletal muscle specific E3 ligases of protein ubiquitin-proteasome system (UPS), was accordingly up-regulated, and the reduced MyHC was significantly mitigated by MG132, a 26S proteasome inhibitor, indicating a key role of UPS in the protein degradation of muscle cells. Further study showed that Tet induced autophagy also participated in the protein degradation. Mechanistically, Tet treatment caused ROS production in myotubes that in turn targeted on FoxO3/AKT signaling, resulting in the activation of UPS and autophagy processes that were involved in the protein degradation. Our study reveals a potential side-effect of Tet on skeletal muscle atrophy, particularly when the drug dose is relatively high.

Knockout of the Muscle-Specific E3 Ligase MuRF1 Affects Liver Lipid Metabolism upon Dexamethasone Treatment in Mice

In order to preserve muscle mass during catabolic states, investigators are actively searching for a specific inhibitor of MuRF1, the only known E3 ligase that can target muscle contractile proteins for their degradation. However, what would be the consequences of such inhibitors on other organs, both in the short and long term? Indeed, skeletal muscles can provide amino acids for liver gluconeogenesis, which is a crucial adaptation for maintaining glucose homeostasis upon elevated energy demands (e.g., during prolonged starvation). Comparing 3-month-old wild-type and MuRF1-KO mice, we measured tissue weights, liver glycogen, lipid and protein content, and liver biochemical composition using Fourier transform infrared (FTIR) spectrometry in control animals and in dexamethasone (Dex)-treated animals. Dex induces a catabolic situation with muscle atrophy and lipid deposits in the liver. In response to Dex treatment, liver glycogen, lipid, and protein content increased in wild type (WT) and MuRF1-KO mice. We found that MuRF1 deletion differentially affected organ weights, the liver of KO mice being hypertrophied upon Dex treatment when compared to WT mice. Upon Dex treatment, muscle mass was preserved in MuRF1-KO mice, and by contrast, liver lipid content increased more in these animals than in WT mice. PLS-DA analysis of FTIR showed that the levels of 13 markers were significantly altered in KO vs WT mice, witnessing profound alterations of lipid, protein, and glycogen content in the liver due to the absence of MuRF1. Using Nile red and oil red lipid staining, we also found that both membrane-linked lipids and intracellular lipid droplets were altered due to the absence of MuRF1. Altogether, it seems that when the liver is deprived of the possibility of obtaining amino acids from muscle upon Dex treatment, there is a concomitant increase in tissue weight and anabolic activity.

Therapeutic potential of omaveloxolone in counteracting muscle atrophy post-denervation: a multi-omics approach

BACKGROUND

Muscle atrophy caused by denervation is common in neuromuscular diseases, leading to loss of muscle mass and function. However, a comprehensive understanding of the overall molecular network changes during muscle denervation atrophy is still deficient, hindering the development of effective treatments.

METHOD

In this study, a sciatic nerve transection model was employed in male C57BL/6 J mice to induce muscle denervation atrophy. Gastrocnemius muscles were harvested at 3 days, 2 weeks, and 4 weeks post-denervation for transcriptomic and proteomic analysis. An integrative multi-omics approach was utilized to identify key genes essential for disease progression. Targeted proteomics using PRM was then employed to validate the differential expression of central genes. Combine single-nucleus sequencing results to observe the expression levels of PRM-validated genes in different cell types within muscle tissue.Through upstream regulatory analysis, NRF2 was identified as a potential therapeutic target. The therapeutic potential of the NRF2-targeting drug Omaveloxolone was evaluated in the mouse model.

RESULT

This research examined the temporal alterations in transcripts and proteins during muscle atrophy subsequent to denervation. A comprehensive analysis identified 54,534 transcripts and 3,218 proteins, of which 23,282 transcripts and 1,852 proteins exhibited statistically significant changes at 3 days, 2 weeks, and 4 weeks post-denervation. Utilizing multi-omics approaches, 30 hubgenes were selected, and PRM validation confirmed significant expression variances in 23 genes. The findings highlighted the involvement of mitochondrial dysfunction, oxidative stress, and metabolic disturbances in the pathogenesis of muscle atrophy, with a pronounced impact on type II muscle fibers, particularly type IIb fibers. The potential therapeutic benefits of Omaveloxolone in mitigating oxidative stress and preserving mitochondrial morphology were confirmed, thereby presenting novel strategies for addressing muscle atrophy induced by denervation. GSEA analysis results show that Autophagy, glutathione metabolism, and PPAR signaling pathways are significantly upregulated, while inflammation-related and neurodegenerative disease-related pathways are significantly inhibited in the Omaveloxolone group.GSR expression and the GSH/GSSG ratio were significantly higher in the Omaveloxolone group compared to the control group, while MuSK expression was significantly lower than in the control group.

CONCLUSION

In our study, we revealed the crucial role of oxidative stress, glucose metabolism, and mitochondrial dysfunction in denervation-induced muscle atrophy, identifying NRF2 as a potential therapeutic target. Omaveloxolone was shown to stabilize mitochondrial function, enhance antioxidant capacity, and protect neuromuscular junctions, thereby offering promising therapeutic potential for treating denervation-induced muscle atrophy.

Therapeutic targeting of GDF11 in muscle atrophy: Insights and strategies

The exploration of novel therapeutic avenues for skeletal muscle atrophy is imperative due to its significant health impact. Recent studies have spotlighted growth differentiation factor 11 (GDF11), a TGFβ superfamily member, for its rejuvenating role in reversing age-related tissue dysfunction. This review synthesizes current findings on GDF11, elucidating its distinct biological functions and the ongoing debates regarding its efficacy in muscle homeostasis. By addressing discrepancies in current research outcomes and its ambiguous role due to its homological identity to myostatin, a negative regulator of muscle mass, this review aims to clarify the role of GDF11 in muscle homeostasis and its potential as a therapeutic target for muscle atrophy. Through a thorough examination of GDF11's mechanisms and effects, this review provides insights that could pave the way for innovative treatments for muscle atrophy, emphasizing the need and strategies to boost endogenous GDF11 levels for therapeutic potential.

Activation of the apelin/APJ system by vitamin D attenuates age-related muscle atrophy

AIMS

Age-related frailty and reduced physical activity contribute to a degenerative loss of muscle mass, function, and strength, which is known as sarcopenia. Increasing evidence has shown that vitamin D has beneficial effects on the muscle health. However, the molecular mechanisms of vitamin D have not been fully elucidated. In this study, we aimed to demonstrate whether vitamin D can overcome muscle atrophy due to aging, especially with respect to the regulation of myokines.

MAIN METHODS

Young (3-month-old) and aged (18-month-old) C57BL/6 mice were assigned to the following 3 groups: normal diet (1000 IU/kg), vitamin D3-supplemented diet (20,000 IU/kg), and normal diet plus exercise for 4 months.

KEY FINDINGS

We found that the reduction in muscle strength and mass due to aging was reversed by vitamin D3 supplementation. The levels of markers involved in muscle atrophy and cellular senescence in the muscle of the aged mice were substantially decreased by vitamin D3. Interestingly, we observed that the expression of apelin and its receptor (APJ), which is known to be secreted after exercise, significantly increased in aged muscles with a vitamin D3-supplemented diet but not in the young mice. Moreover, circulating interleukin-6 (IL-6) and growth differentiation factor 8 (GDF8) levels were significantly increased in the aged mice but were restored by vitamin D3 treatment.

SIGNIFICANCE

Our present data indicate that vitamin D3 supplementation ameliorates aging-induced muscle atrophy and senescence, similar to the effects of exercise, suggesting the positive impact of vitamin D as an intervention strategy to prevent aging-induced metabolic diseases.

Molecular regulation of reversible cardiac remodeling: lessons from species with extreme physiological adaptations

Some vertebrates evolved to have a remarkable capacity for anatomical and physiological plasticity in response to environmental challenges. One example of such plasticity can be found in the ambush-hunting snakes of the genus Python, which exhibit reversible cardiac growth with feeding. The predation strategy employed by pythons is associated with months-long fasts that are arrested by ingestion of large prey. Consequently, digestion compels a dramatic increase in metabolic rate and hypertrophy of multiple organs, including the heart. In this Review, we summarize the post-prandial cardiac adaptations in pythons at the whole-heart, cellular and molecular scales. We highlight circulating factors and cellular signaling pathways that are altered during digestion to affect cardiac form and function and propose possible mechanisms that may drive the post-digestion regression of cardiac mass. Adaptive physiological cardiac hypertrophy has also been observed in other vertebrates, including in fish acclimated to cold water, birds flying at high altitudes and exercising mammals. To reveal potential evolutionarily conserved features, we summarize the molecular signatures of reversible cardiac remodeling identified in these species and compare them with those of pythons. Finally, we offer a perspective on the potential of biomimetics targeting the natural biology of pythons as therapeutics for human heart disease.

Regression of postprandial cardiac hypertrophy in burmese pythons is mediated by FoxO1

As ambush-hunting predators that consume large prey after long intervals of fasting, Burmese pythons evolved with unique adaptations for modulating organ structure and function. Among these is cardiac hypertrophy that develops within three days following a meal (Andersen et al., 2005, Secor, 2008), which we previously showed was initiated by circulating growth factors (Riquelme et al., 2011). Postprandial cardiac hypertrophy in pythons also rapidly regresses with subsequent fasting (Secor, 2008); however, the molecular mechanisms that regulate the dynamic cardiac remodeling in pythons during digestion are largely unknown. In this study, we employed a multiomics approach coupled with targeted molecular analyses to examine remodeling of the python ventricular transcriptome and proteome throughout digestion. We found that forkhead box protein O1 (FoxO1) signaling was suppressed prior to hypertrophy development and then activated during regression, which coincided with decreased and then increased expression, respectively, of FoxO1 transcriptional targets involved in proteolysis. To define the molecular mechanistic role of FoxO1 in hypertrophy regression, we used cultured mammalian cardiomyocytes treated with postfed python plasma. Hypertrophy regression both in pythons and in vitro coincided with activation of FoxO1-dependent autophagy; however, the introduction of a FoxO1-specific inhibitor prevented both regression of cell size and autophagy activation. Finally, to determine whether FoxO1 activation could induce regression, we generated an adenovirus expressing a constitutively active FoxO1. FoxO1 activation was sufficient to prevent and reverse postfed plasma-induced hypertrophy, which was partially prevented by autophagy inhibition. Our results indicate that modulation of FoxO1 activity contributes to the dynamic ventricular remodeling in postprandial Burmese pythons.

Autophagy is a promising process for linking inflammation and redox homeostasis in Down syndrome

Trisomy 21, characterized by the presence of an additional chromosome 21, leads to a set of clinical features commonly referred to as Down syndrome (DS). The pathological phenotypes observed in DS are caused by a combination of factors, such as mitochondrial dysfunction, neuroinflammation, oxidative stress, disrupted metabolic patterns, and changes in protein homeostasis and signal transduction, and these factors collectively induce neurological alterations. In DS, the triplication of chromosome 21 and the micronuclei arising from the missegregation of chromosomes are closely associated with inflammation and the development of redox imbalance. Autophagy, an essential biological process that affects cellular homeostasis, is a powerful tool to facilitate the degradation of redundant or dysfunctional cytoplasmic components, thereby enabling the recycling of their constituents. Targeting the autophagy process has been suggested as a promising method to balance intracellular inflammation and oxidative stress and improve mitochondrial dysfunction. In this review, we summarize the role of autophagy in regulating inflammation and redox homeostasis in DS and discuss their crosslinks. A comprehensive elucidation of the roles of autophagy in DS offers novel insights for the development of therapeutic strategies aimed at aneuploidy-associated diseases.

KLF13 restrains Dll4-muscular Notch2 axis to improve the muscle atrophy

BACKGROUND

Muscle atrophy can cause muscle dysfunction and weakness. Krüppel-like factor 13 (KLF13), a central regulator of cellular energy metabolism, is highly expressed in skeletal muscles and implicated in the pathogenesis of several diseases. This study investigated the role of KLF13 in muscle atrophy, which could be a novel therapeutic target.

METHODS

The effects of gene knockdown and pharmacological targeting of KLF13 on skeletal muscle atrophy were investigated using cell-based and animal models. Clofoctol, an antibiotic and KLF13 agonist, was also investigated as a candidate for repurposing. The mechanisms related to skeletal muscle atrophy were assessed by measuring the expression levels and activation statuses of key regulatory pathways and validated using gene knockdown and RNA sequencing.

RESULTS

In a dexamethasone-induced muscle atrophy mouse model, the KLF13 knockout group had decreased muscle strength (N) (1.77 ± 0.10 vs. 1.48 ± 0.16, P < 0.01), muscle weight (%) [gastrocnemius (Gas): 76.0 ± 5.69 vs. 60.7 ± 7.23, P < 0.001; tibialis anterior (TA): 75.8 ± 6.21 vs. 67.5 ± 5.01, P < 0.05], and exhaustive running distance (m) (495.5 ± 64.8 vs. 315.5 ± 60.9, P < 0.05) compared with the control group. KLF13 overexpression preserved muscle mass (Gas: 100 ± 6.38 vs. 120 ± 14.4, P < 0.01) and the exhaustive running distance (423.8 ± 59.04 vs. 530.2 ± 77.45, P < 0.05) in an in vivo diabetes-induced skeletal muscle atrophy model. Clofoctol treatment protected against dexamethasone-induced muscle atrophy. Myotubes treated with dexamethasone, an atrophy-inducing glucocorticoid, were aggravated by KLF13 knockout, but anti-atrophic effects were achieved by inducing KLF13 overexpression. We performed a transcriptome analysis and luciferase reporter assays to further explore this mechanism, finding that delta-like 4 (Dll4) was a novel target gene of KLF13. The KLF13 transcript repressed Dll4, inhibiting the Dll4-Notch2 axis and preventing muscle atrophy. Dexamethasone inhibited KLF13 expression by inhibiting myogenic differentiation 1 (i.e., MYOD1)-mediated KLF13 transcriptional activation and promoting F-Box and WD repeat domain containing 7 (i.e., FBXW7)-mediated KLF13 ubiquitination.

CONCLUSIONS

This study sheds new light on the mechanisms underlying skeletal muscle atrophy and potential drug targets. KLF13 regulates muscle atrophy and is a potential therapeutic target. Clofoctol is an attractive compound for repurposing studies to treat skeletal muscle atrophy.

The role of ZEB1 in mediating the protective effects of metformin on skeletal muscle atrophy

Metformin is an important antidiabetic drug that has the potential to reduce skeletal muscle atrophy and promote the differentiation of muscle cells. However, the exact molecular mechanism underlying these functions remains unclear. Previous studies revealed that the transcription factor zinc finger E-box-binding homeobox 1 (ZEB1), which participates in tumor progression, inhibits muscle atrophy. Therefore, we hypothesized that the protective effect of metformin might be related to ZEB1. We investigated the positive effect of metformin on IL-1β-induced skeletal muscle atrophy by regulating ZEB1 in vitro and in vivo. Compared with the normal cell differentiation group, the metformin-treated group presented increased myotube diameters and reduced expression levels of atrophy-marker proteins. Moreover, muscle cell differentiation was hindered, when we artificially interfered with ZEB1 expression in mouse skeletal myoblast (C2C12) cells via ZEB1-specific small interfering RNA (si-ZEB1). In response to inflammatory stimulation, metformin treatment increased the expression levels of ZEB1 and three differentiation proteins, MHC, MyoD, and myogenin, whereas si-ZEB1 partially counteracted these effects. Moreover, marked atrophy was induced in a mouse model via the administration of lipopolysaccharide (LPS) to the skeletal muscles of the lower limbs. Over a 4-week period of intragastric administration, metformin treatment ameliorated muscle atrophy and increased the expression levels of ZEB1. Metformin treatment partially alleviated muscle atrophy and stimulated differentiation. Overall, our findings may provide a better understanding of the mechanism underlying the effects of metformin treatment on skeletal muscle atrophy and suggest the potential of metformin as a therapeutic drug.

Loss of SELENOW aggravates muscle loss with regulation of protein synthesis and the ubiquitin-proteasome system

Sarcopenia is characterized by accelerated muscle mass and function loss, which burdens and challenges public health worldwide. Several studies indicated that selenium deficiency is associated with sarcopenia; however, the specific mechanism remains unclear. Here, we demonstrated that selenoprotein W (SELENOW) containing selenium in the form of selenocysteine functioned in sarcopenia. SELENOW expression is up-regulated in dexamethasone (DEX)-induced muscle atrophy and age-related sarcopenia mouse models. Knockout (KO) of SELENOW profoundly aggravated the process of muscle mass loss in the two mouse models. Mechanistically, SELENOW KO suppressed the RAC1-mTOR cascade by the interaction between SELENOW and RAC1 and induced the imbalance of protein synthesis and degradation. Consistently, overexpression of SELENOW in vivo and in vitro alleviated the muscle and myotube atrophy induced by DEX. SELENOW played a role in age-related sarcopenia and regulated the genes associated with aging. Together, our study uncovered the function of SELENOW in age-related sarcopenia and provides promising evidence for the prevention and treatment of sarcopenia.

Dysregulated FOXO1 activity drives skeletal muscle intrinsic dysfunction in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a multisystemic neurodegenerative disorder, with accumulating evidence indicating metabolic disruptions in the skeletal muscle preceding disease symptoms, rather than them manifesting as a secondary consequence of motor neuron (MN) degeneration. Hence, energy homeostasis is deeply implicated in the complex physiopathology of ALS and skeletal muscle has emerged as a key therapeutic target. Here, we describe intrinsic abnormalities in ALS skeletal muscle, both in patient-derived muscle cells and in muscle cell lines with genetic knockdown of genes related to familial ALS, such as TARDBP (TDP-43) and FUS. We found a functional impairment of myogenesis that parallels defects of glucose oxidation in ALS muscle cells. We identified FOXO1 transcription factor as a key mediator of these metabolic and functional features in ALS muscle, via gene expression profiling and biochemical surveys in TDP-43 and FUS-silenced muscle progenitors. Strikingly, inhibition of FOXO1 mitigated the impaired myogenesis in both the genetically modified and the primary ALS myoblasts. In addition, specific in vivo conditional knockdown of TDP-43 or FUS orthologs (TBPH or caz) in Drosophila muscle precursor cells resulted in decreased innervation and profound dysfunction of motor nerve terminals and neuromuscular synapses, accompanied by motor abnormalities and reduced lifespan. Remarkably, these phenotypes were partially corrected by foxo inhibition, bolstering the potential pharmacological management of muscle intrinsic abnormalities associated with ALS. The findings demonstrate an intrinsic muscle dysfunction in ALS, which can be modulated by targeting FOXO factors, paving the way for novel therapeutic approaches that focus on the skeletal muscle as complementary target tissue.

Induction of DEPP1 by HIF Mediates Multiple Hallmarks of Ischemic Cardiomyopathy

BACKGROUND

HIF (hypoxia inducible factor) regulates many aspects of cardiac function. We and others previously showed that chronic HIF activation in the heart in mouse models phenocopies multiple features of ischemic cardiomyopathy in humans, including mitochondrial loss, lipid accumulation, and systolic cardiac dysfunction. In some settings, HIF also causes the loss of peroxisomes. How, mechanistically, HIF promotes cardiac dysfunction is an open question.

METHODS

We used mice lacking cardiac pVHL (von Hippel-Lindau protein) to investigate how chronic HIF activation causes multiple features of ischemic cardiomyopathy, such as autophagy induction and lipid accumulation. We performed immunoblot assays, RNA sequencing, mitochondrial and peroxisomal autophagy flux measurements, and live cell imaging on isolated cardiomyocytes. We used CRISPR-Cas9 gene editing in mice to validate a novel mediator of cardiac dysfunction in the setting of chronic HIF activation.

RESULTS

We identify a previously unknown pathway by which cardiac HIF activation promotes the loss of mitochondria and peroxisomes. We found that DEPP1 (decidual protein induced by progesterone 1) is induced under hypoxia in a HIF-dependent manner and localizes inside mitochondria. DEPP1 is both necessary and sufficient for hypoxia-induced autophagy and triglyceride accumulation in cardiomyocytes ex vivo. DEPP1 loss increases cardiomyocyte survival in the setting of chronic HIF activation ex vivo, and whole-body Depp1 loss decreases cardiac dysfunction in hearts with chronic HIF activation caused by VHL loss in vivo.

CONCLUSIONS

Our findings identify DEPP1 as a key component in the cardiac remodeling that occurs with chronic ischemia.

Autophagy in aging-related diseases and cancer: Principles, regulatory mechanisms and therapeutic potential

Macroautophagy/autophagy is primarily accountable for the degradation of damaged organelles and toxic macromolecules in the cells. Regarding the essential function of autophagy for preserving cellular homeostasis, changes in, or dysfunction of, autophagy flux can lead to disease development. In the current paper, the complicated function of autophagy in aging-associated pathologies and cancer is evaluated, highlighting the underlying molecular mechanisms that can affect longevity and disease pathogenesis. As a natural biological process, a reduction in autophagy is observed with aging, resulting in an accumulation of cell damage and the development of different diseases, including neurological disorders, cardiovascular diseases, and cancer. The MTOR, AMPK, and ATG proteins demonstrate changes during aging, and they are promising therapeutic targets. Insulin/IGF1, TOR, PKA, AKT/PKB, caloric restriction and mitochondrial respiration are vital for lifespan regulation and can modulate or have an interaction with autophagy. The specific types of autophagy, such as mitophagy that degrades mitochondria, can regulate aging by affecting these organelles and eliminating those mitochondria with genomic mutations. Autophagy and its specific types contribute to the regulation of carcinogenesis and they are able to dually enhance or decrease cancer progression. Cancer hallmarks, including proliferation, metastasis, therapy resistance and immune reactions, are tightly regulated by autophagy, supporting the conclusion that autophagy is a promising target in cancer therapy.

A molecular pathway for cancer cachexia-induced muscle atrophy revealed at single-nucleus resolution

Cancer cachexia is a prevalent and often fatal wasting condition that cannot be fully reversed with nutritional interventions. Muscle atrophy is a central component of the syndrome, but the mechanisms whereby cancer leads to skeletal muscle atrophy are not well understood. We performed single-nucleus multi-omics on skeletal muscles from a mouse model of cancer cachexia and profiled the molecular changes in cachexic muscle. Our results revealed the activation of a denervation-dependent gene program that upregulates the transcription factor myogenin. Further studies showed that a myogenin-myostatin pathway promotes muscle atrophy in response to cancer cachexia. Short hairpin RNA inhibition of myogenin or inhibition of myostatin through overexpression of its endogenous inhibitor follistatin prevented cancer cachexia-induced muscle atrophy in mice. Our findings uncover a molecular basis of muscle atrophy associated with cancer cachexia and highlight potential therapeutic targets for this disorder.

Anoikis-Related Genes Impact Prognosis and Tumor Microenvironment in Bladder Cancer

Anoikis tolerance is an important biological process of tumor colonization and metastasis outside the primary tumor. Recent research has progressively elucidated the function and underlying mechanisms of anoikis in the metastasis of various solid tumors. Nevertheless, the specific mechanisms of anoikis in bladder cancer and its consequent effects on the tumor immune microenvironment remain ambiguous. In this study, we developed an anoikis score based on five genes (ETV7, NGF, SCD, LAMC1, and CASP6) and categorized subjects into high and low-risk groups using the median score from the TCGA database. Our findings indicate that SCD enhances the proliferation of bladder cancer cells in vitro. Furthermore, integrating the anoikis score with clinicopathological features to construct a prognostic nomogram demonstrated precision in assessing patient outcomes. Immune cell analysis revealed elevated infiltration levels of Treg cells and M2 macrophages in the high anoikis score group, whereas CD8+ T cell levels were reduced. This study highlights the importance of anoikis score in predicting patient prognosis, immune cell infiltration, and drug response, which may provide a treatment modality worth exploring in depth for the study of bladder cancer.

Ubiquitination Insight from Spinal Muscular Atrophy-From Pathogenesis to Therapy: A Muscle Perspective

Spinal muscular atrophy (SMA) is one of the most frequent causes of death in childhood. The disease's molecular basis is deletion or mutations in the SMN1 gene, which produces reduced survival motor neuron protein (SMN) levels. As a result, there is spinal motor neuron degeneration and a large increase in muscle atrophy, in which the ubiquitin-proteasome system (UPS) plays a significant role. In humans, a paralogue of SMN1, SMN2 encodes the truncated protein SMNΔ7. Structural differences between SMN and SMNΔ7 affect the interaction of the proteins with UPS and decrease the stability of the truncated protein. SMN loss affects the general ubiquitination process by lowering the levels of UBA1, one of the main enzymes in the ubiquitination process. We discuss how SMN loss affects both SMN stability and the general ubiquitination process, and how the proteins involved in ubiquitination could be used as future targets for SMA treatment.

Proteasome gene expression is controlled by coordinated functions of multiple transcription factors

Proteasome activity is crucial for cellular integrity, but how tissues adjust proteasome content in response to catabolic stimuli is uncertain. Here, we demonstrate that transcriptional coordination by multiple transcription factors is required to increase proteasome content and activate proteolysis in catabolic states. Using denervated mouse muscle as a model system for accelerated proteolysis in vivo, we reveal that a two-phase transcriptional program activates genes encoding proteasome subunits and assembly chaperones to boost an increase in proteasome content. Initially, gene induction is necessary to maintain basal proteasome levels, and in a more delayed phase (7-10 days after denervation), it stimulates proteasome assembly to meet cellular demand for excessive proteolysis. Intriguingly, the transcription factors PAX4 and α-PALNRF-1 control the expression of proteasome among other genes in a combinatorial manner, driving cellular adaptation to muscle denervation. Consequently, PAX4 and α-PALNRF-1 represent new therapeutic targets to inhibit proteolysis in catabolic diseases (e.g., type-2 diabetes, cancer).

Impact of Selected Glucagon-like Peptide-1 Receptor Agonists on Serum Lipids, Adipose Tissue, and Muscle Metabolism-A Narrative Review

Glucagon-like peptide-1 receptor agonists (GLP-1 RA) are novel antihyperglycemic agents. By acting through the central nervous system, they increase satiety and reduce food intake, thus lowering body weight. Furthermore, they increase the secretion of insulin while decreasing the production of glucagon. However, recent studies suggest a more complex metabolic impact through the interaction with various other tissues. In our present review, we aim to provide a summary of the effects of GLP-1 RA on serum lipids, adipose tissue, and muscle metabolism. It has been found that GLP-1 RA therapy is associated with decreased serum cholesterol levels. Epicardial adipose tissue thickness, hepatic lipid droplets, and visceral fat volume were reduced in obese patients with cardiovascular disease. GLP-1 RA therapy decreased the level of proinflammatory adipokines and reduced the expression of inflammatory genes. They have been found to reduce endoplasmic reticulum stress in adipocytes, leading to better adipocyte function and metabolism. Furthermore, GLP-1 RA therapy increased microvascular blood flow in muscle tissue, resulting in increased myocyte metabolism. They inhibited muscle atrophy and increased muscle mass and function. It was also observed that the levels of muscle-derived inflammatory cytokines decreased, and insulin sensitivity increased, resulting in improved metabolism. However, some clinical trials have been conducted on a very small number of patients, which limits the strength of these observations.

The association between the triglyceride-glucose index and sarcopenia: data from the NHANES 2011-2018

BACKGROUND

The Triglyceride-glucose (TyG) index is a marker of insulin resistance, but its role in sarcopenia is controversial. The purpose of this study was to investigate the association of the TyG index with sarcopenia.

METHODS

4030 participants aged 20 years and above were selected from National Health and Nutrition Examination Survey for cross sectional study. Weighted logistic regression model was used to estimate the association between TyG index and sarcopenia. Threshold effect analysis and restricted cubic spline were employed to describe nonlinear link, with interaction tests and subgroup analyses performed.

RESULTS

It was found in the fully adjusted model that the TyG index was positively associated with sarcopenia (per 1-unit increase in the TyG index: OR = 1.31, 95%CI: 1.07, 1.60). This association was further highlighted in groups characterized by the absence of MetS or diabetes, as well as the absence of vigorous or moderate work activity. Furthermore, analysis of the curve fitting and threshold effects indicated a nonlinear relationship, which exhibited a turning point at 9.14.

CONCLUSION

The study results indicated that the TyG index was positively associated with sarcopenia. Enhancing the management of insulin resistance could help reduce the risk of developing sarcopenia.

Resveratrol and Vitamin D: Eclectic Molecules Promoting Mitochondrial Health in Sarcopenia

Sarcopenia refers to the progressive loss and atrophy of skeletal muscle function, often associated with aging or secondary to conditions involving systemic inflammation, oxidative stress, and mitochondrial dysfunction. Recent evidence indicates that skeletal muscle function is not only influenced by physical, environmental, and genetic factors but is also significantly impacted by nutritional deficiencies. Natural compounds with antioxidant properties, such as resveratrol and vitamin D, have shown promise in preventing mitochondrial dysfunction in skeletal muscle cells. These antioxidants can slow down muscle atrophy by regulating mitochondrial functions and neuromuscular junctions. This review provides an overview of the molecular mechanisms leading to skeletal muscle atrophy and summarizes recent advances in using resveratrol and vitamin D supplementation for its prevention and treatment. Understanding these molecular mechanisms and implementing combined interventions can optimize treatment outcomes, ensure muscle function recovery, and improve the quality of life for patients.

Phase-specific outcmes of arginine or branched-chain amino acids supplementation in low crude protein diets on performance, nutrient digestibility, and expression of tissue protein synthesis and degradation in broiler chickens infected with mixed Eimeria spp

A 35-d study investigated the impact of dietary supplementation with Arginine (Arg) or branched-chain amino acids (BCAA) of broilers receiving low-protein diets whilst infected with mixed Eimeria species. All birds were given the same starter (d0-10) and finisher (d28-35) diets. The 4 grower diets used were a positive control (PC) with adequate protein (18.5%), a low protein diet (NC;16.5% CP), or the NC supplemented with Arg or BCAA. Supplemental AA was added at 50% above the recommended levels. The treatments were in a 4 × 2 factorial arrangement, with 4 diets, with or without Eimeria inoculation on d14. Birds and feed were weighed after inoculation in phases: prepatent (d14-17), acute (d18-21), recovery (d22-28), and compensatory (d29-35). Ileal digesta, jejunum, and breast tissue were collected on d21, 28, and 35. There was no diet × Eimeria inoculation on growth performance at any phase. Infected birds weighed less and consumed less feed (P < 0.05) in all phases. In the prepatent and acute phases, birds on the Arg diets had higher weight gain (P < 0.05) and lower FCR, similar to PC, when compared to NC and BCAA-fed ones. Infection reduced AA digestibility on d21 and 28 (Met and Cys). However, birds that received supplemental AA had higher digestibility (P < 0.05) of their respective supplemented AA on d 21 only. Infected birds had lower (P < 0.05) BO + AT and higher PEPT1 expression on d21. There was a diet × Eimeria interaction (P = 0.004) on gene expression at d28; 4EBP1 genes were significantly downwardly expressed (P < 0.05) in birds fed Arg diet, irrespective of infection. Infected birds exhibited an upward expression (P < 0.05) of Eef2 on d21 and d28 but experienced a downward expression on d35. Supplemental Arg and BCAA had variable effects on growth performance, apparent ileal AA digestibility, and genes of protein synthesis and degradation, but the effect of Arg on promoting weight gain, irrespective of the Eimeria challenge, was more consistent.

Loss of function of phosphatidylserine synthase causes muscle atrophy in Drosophila

Maintenance of appropriate muscle mass is crucial for physical activity and metabolism. Aging and various pathological conditions can cause sarcopenia, a condition characterized by muscle mass decline. Although sarcopenia has been actively studied, the mechanisms underlying muscle atrophy are not well understood. Thus, we aimed to investigate the role of Phosphatidylserine synthase (Pss) in muscle development and homeostasis in Drosophila. The results showed that muscle-specific Pss knockdown decreased exercise capacity and produced sarcopenic phenotypes. In addition, it increased the apoptosis rate because of the elevated reactive oxygen species production resulting from mitochondrial dysfunction. Moreover, the autophagy rate increased due to increased FoxO activity caused by reduced Akt activity. Collectively, these findings demonstrate that enhanced apoptosis and autophagy rates resulting from muscle-specific Pss knockdown jointly contribute to sarcopenia development, highlighting the key role of the PSS pathway in muscle health.

C16ORF70/MYTHO promotes healthy aging in C.elegans and prevents cellular senescence in mammals

The identification of genes that confer either extension of life span or accelerate age-related decline was a step forward in understanding the mechanisms of aging and revealed that it is partially controlled by genetics and transcriptional programs. Here, we discovered that the human DNA sequence C16ORF70 encodes a protein, named MYTHO (macroautophagy and youth optimizer), which controls life span and health span. MYTHO protein is conserved from Caenorhabditis elegans to humans and its mRNA was upregulated in aged mice and elderly people. Deletion of the orthologous myt-1 gene in C. elegans dramatically shortened life span and decreased animal survival upon exposure to oxidative stress. Mechanistically, MYTHO is required for autophagy likely because it acts as a scaffold that binds WIPI2 and BCAS3 to recruit and assemble the conjugation system at the phagophore, the nascent autophagosome. We conclude that MYTHO is a transcriptionally regulated initiator of autophagy that is central in promoting stress resistance and healthy aging.

The Impact of Ulmus macrocarpa Extracts on a Model of Sarcopenia-Induced C57BL/6 Mice

Aging leads to tissue and cellular changes, often driven by oxidative stress and inflammation, which contribute to age-related diseases. Our research focuses on harnessing the potent anti-inflammatory and antioxidant properties of Korean Ulmus macrocarpa Hance, a traditional herbal remedy, to address muscle loss and atrophy. We evaluated the effects of Ulmus extract on various parameters in a muscle atrophy model, including weight, exercise performance, grip strength, body composition, muscle mass, and fiber characteristics. Additionally, we conducted Western blot and RT-PCR analyses to examine muscle protein regulation, apoptosis factors, inflammation, and antioxidants. In a dexamethasone-induced muscle atrophy model, Ulmus extract administration promoted genes related to muscle formation while reducing those associated with muscle atrophy. It also mitigated inflammation and boosted muscle antioxidants, indicating a potential improvement in muscle atrophy. These findings highlight the promise of Ulmus extract for developing pharmaceuticals and supplements to combat muscle loss and atrophy, paving the way for clinical applications.

CARM1 drives mitophagy and autophagy flux during fasting-induced skeletal muscle atrophy

CARM1 (coactivator associated arginine methyltransferase 1) has recently emerged as a powerful regulator of skeletal muscle biology. However, the molecular mechanisms by which the methyltransferase remodels muscle remain to be fully understood. In this study, carm1 skeletal muscle-specific knockout (mKO) mice exhibited lower muscle mass with dysregulated macroautophagic/autophagic and atrophic signaling, including depressed AMP-activated protein kinase (AMPK) site-specific phosphorylation of ULK1 (unc-51 like autophagy activating kinase 1; Ser555) and FOXO3 (forkhead box O3; Ser588), as well as MTOR (mechanistic target of rapamycin kinase)-induced inhibition of ULK1 (Ser757), along with AKT/protein kinase B site-specific suppression of FOXO1 (Ser256) and FOXO3 (Ser253). In addition to lower mitophagy and autophagy flux in skeletal muscle, carm1 mKO led to increased mitochondrial PRKN/parkin accumulation, which suggests that CARM1 is required for basal mitochondrial turnover and autophagic clearance. carm1 deletion also elicited PPARGC1A (PPARG coactivator 1 alpha) activity and a slower, more oxidative muscle phenotype. As such, these carm1 mKO-evoked adaptations disrupted mitophagy and autophagy induction during food deprivation and collectively served to mitigate fasting-induced muscle atrophy. Furthermore, at the threshold of muscle atrophy during food deprivation experiments in humans, skeletal muscle CARM1 activity decreased similarly to our observations in mice, and was accompanied by site-specific activation of ULK1 (Ser757), highlighting the translational impact of the methyltransferase in human skeletal muscle. Taken together, our results indicate that CARM1 governs mitophagic, autophagic, and atrophic processes fundamental to the maintenance and remodeling of muscle mass. Targeting the enzyme may provide new therapeutic approaches for mitigating skeletal muscle atrophy.Abbreviation: ADMA: asymmetric dimethylarginine; AKT/protein kinase B: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ATG: autophagy related; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; CARM1: coactivator associated arginine methyltransferase 1; Col: colchicine; CSA: cross-sectional area; CTNS: cystinosin, lysosomal cystine transporter; EDL: extensor digitorum longus; FBXO32/MAFbx: F-box protein 32; FOXO: forkhead box O; GAST: gastrocnemius; H2O2: hydrogen peroxide; IMF: intermyofibrillar; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; mKO: skeletal muscle-specific knockout; MMA: monomethylarginine; MTOR: mechanistic target of rapamycin kinase; MYH: myosin heavy chain; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; OXPHOS: oxidative phosphorylation; PABPC1/PABP1: poly(A) binding protein cytoplasmic 1; PPARGC1A/PGC-1α: PPARG coactivator 1 alpha; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; PRMT: protein arginine methyltransferase; Sal: saline; SDMA: symmetric dimethylarginine; SIRT1: sirtuin 1; SKP2: S-phase kinase associated protein 2; SMARCC1/BAF155: SWI/SNF related, matrix associated, actin dependent regulator of chromatin subfamily c member 1; SOL: soleus; SQSTM1/p62: sequestosome 1; SS: subsarcolemmal; TA: tibialis anterior; TFAM: transcription factor A, mitochondrial; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; TRIM63/MuRF1: tripartite motif containing 63; ULK1: unc-51 like autophagy activating kinase 1; VPS11: VPS11 core subunit of CORVET and HOPS complexes; WT: wild-type.